Polyamide compositions containing a phenol, a phosphate, a manganese salt, and an acid anhydride as stabilisers



of manufacture, as,

United States Patent corporate Filed Nov. 21, 1962, Ser. No.

No Drawing. Claims priority, application Great Britain, Nov.

Claims. (Cl. 260-4555) This invention relates to synthetic polyamidecompositions, to processes for their production and to shaped articles,including textile fibres, made from such compositions.

Polyamides, such as polyhexamethylene adipamide and polycaprolactam, arewidely used for many purposes because of their remarkable mechanicalstrength. Their main field of application is the production of syntheticfibres, but they also find increasing use in other branches for example,in the production of tools and machine parts. The excellent propertiesof these polyamides are, however, considerably impaired by theirtendency to become yellow under various conditions in the presence ofoxygen. The yellowing occurs, for example, when polyarnides aresubjected to elevated temperatures, when they are repeatedly washed withhot water, and when they are exposed to light and then kept for sometime in the dark.

, This sensitiveness of polyamides is especially inconvenent for thetextile industry, where it is desired to obtain fibres and (fabrics of apure white or of coloured shades unimpaired by any yellowish tinge. Itis, therefore, very disturbing that discolouration occurs during somestages of manufacture, e.g. when the molten polyamide is discharged froman autoclave, in melt-spinning, and above all, in the dry heat-settingof spun filaments and of knitted or woven fabrics. The troublesomeyellowing which appears during these processes may be partially removedby a bleaching treatment, eg with sodium chlorite, but such treatmentrequires an additional working step and may also be harmful to the fibreor fabric. It is, however, known that bleaching with sodium chlorite,while removing the colour present for the time being, considerablyincreases the tendency of the fibre to future discolouration.

Substances such as phenols and amines, which are antioxidants, have beenproposed as stabilizers as it is generally assumed that oxidation is aprimary cause of the discolouration of poly am-ides. Other substancesdescribed as stabilizers include manganese salts and phosphoruscompounds, and it has also been proposed to use combinations of two ormore stabilizing substances. Thus, United States Patent No. 2,887,462describes the use of salts of manganese with certain reducing acids, andUnited States Patent No. 2,984,647 mentions manganese phosphates.British Patent No. 689,629 proposes manganese or copper salts ofsalicylic or anth-ranilic acid, and French Patent No. 1,099,407 suggestsa combination of manganese and copper salts. All these combinations aredescribed as being efiective against damage by light. As stabilizingagents for polyamides against heat, British Patent No. 652,947 proposescopper salts of mono-carboxylic acids together with diketones, UnitedStates Patent No. 2,705,227 describes a combination of copper, inorganicnear Lucerne, Switzer- Suisse, Emmena Swiss body 3,260,697 Patented July12, 1966 ice halogen salts, and phosphorus compounds, and GermanAuslegeschrift No. 1,111,376 mentions a mixture of cerium (III) and/ ortitanium (Ill) salts and hypophosphoric acids. This German specificationalso points out that the addition of aliphatic oarboxylic acids does notstabilize p-olyarnides against the effects of light or heat. None of theabove-mentioned combinations of stabilizers have, however, yet led toany final and completely satisfactory solution of the problem ofyellowing caused by heat and light.

The present invention provides synthetic polyamide compositions,especially suitable for making textile fibres, which are substantiallyfree from colour and possess a substantial stability againstdiscolouration caused by heat and light. The expression free from colouris used herein to mean absence of any undesired colouration of thepolyamide, but doesnot exclude colour intentionally produced by theaddition of dyes or pigments.

The synthetic polyamide compositions of the invention comprise acomposite stabilizing agent consisting essentially of (l) a thermallystable phenol, (2) a salt or ester of an inorganic phosphorus oxy-acid,(3) a manganese salt, and (4) an organic carboxylic acid anhydride. Itwill, of course, be understood that all the components of thestabilizing agent must be such that they will not themselves give riseto any colour when incorporated in the poly-amide, either because theyare coloured per se or because they give rise to coloured substances onirradiation or heating to the temperatures used during manufacture orprocessing of polyamides. Thus, phthalic anhydride, which is unstable tolight, cannot be used as component (4). The components of thestabilizing agent must comply with the stated limitations. Thus, forexample, simple phenols cannot be used as they are oxidized too quickly,but thermally stabilized phenols containing, e.g. one or more tertiarybutyl groups such as 2,5-di-tert-butyl hydroquinone, 2,2methyl-bis-(4-methyl-G-tert-butylQphenol),2,2-methylene-bis-(4-ethyl-6-tert butyl-phenol), or 4,4ibutylidenebis(6-tert butyl-m-cresol) have been found to be very suitable. As thesecond component, sodium hypophoshite and triphenyl phosphate, which areboth relaible, are preferred. For the manganese salt, manganous lactate,manganous oxalate and manganous hypophosphite are very suitable. As theacid anhydride component, benzoic acid anhydride and hexa-hydro-phthalicacid anhydride are very satisfactory. A further advantage of theinvention is that these acid anhydrides, in addition to acting asstabilizers, act also as chain terminators for the polycondensationprocess for making the polyamides. They can, therefore, replace theacetic acid which is usually employed for this purpose. The conventionaltype of chain terminating mono-oarboxylic acid cannot (as shown in theExample 11 below) be used to replace component (4) in the stabilizingagent of the invention.

The relative quantities of the various components of the stabilizingagent used for optimum results will differ with the specific nature ofthe components. However, combinations giving especially good protectioncontain between 0.02 and 0.2% of 2,5-di-tert butyl-hydro-quinone, 2,2methylene-bis-(4 methyl-6-tert-butyl-phenol), 2,2-methylene-bis-(4-ethyl-6-tertbutylphenol) or 4,4'4butylidenebis-(6-tert-butyl-m-cresol), between 0.05 and 0.5% of sodiumhypophosp'hite or triphenyl phosphate, between 20 and parts of manganeseper million parts of polyamide in the form of m-ang-aneous lactate,manganous oxalate, or man-ganous hylpophosph-ite, and between 0.2 andacteristic of this that afforded by any of the components taken alone.As shown in Example II, combinations containing only three of the notgive the same satisfactory results.

The stabilizers have the further advantage that they work well in thepresence of titanium dioxide, which is usually incorporated inpolyamides as a delustering pigment and which is known to increaseconsiderably their sensitivity to light. Dyeing and addition of opticalbrightening agents do not impair the effects of the stabilizercombination of this turbed by its presence in the polyamide.

The excellent protection afforded by the new four-component stabilizeragainst heat is especially important in the textile industry, becausepolyamides are necessarily heated at several stages in the manufactureof textile fibres. Although poly-condensation is carried out in anitrogen atmosphere, traces of oxygen are still present, and, in anycase, oxidation is possible when the molten mass is discharged from anautoclave or extruded from a spinneret. Unprotected polyamide chips andfi'bres have, therefore, a distinct ivory colour, while compositionscontaining the four-component stabilizing agent of the presentdelustered. Further discolouration polyamides usually occurs in the dryheat-setting process, and this operation causes considerable yellowingof unprotected fibres and makes an additional bleaching treatmentnecessary. It is, of great value that polyamide fibres and fabricsproduced in accordance with the present invention do not need bleaching,that they possess and keep a bright, pure white, and that when dyed,they preserve a clear and distinct colour shade foils, tools, and manyother goods.

The four components of the stabilizing agent are incorporated in thepolyamides during tion process of manufacture of the polyamides, and thestabilizers.

The reasons for the discolouration of polyamides have not yet beenfinally ascertained, but the surprisingly good protection afforded bythe use of radicals formed from traces of impurities under the influenceof heat or light. These radicals are oxidized in the presence of air toperoxides which, in turn, trigger the formation of polyamide peroxides.The decomposition of the polyamide peroxides then leads to unsaturatedcompounds which react with free amine end groups with the formation ofheterocyclic substances, e.g. pyrroles. The pyrroles finally react bycondensation with keto-enol groups in the polyamide, thus producing theactual yellow-coloured materials.

Such a view of the reaction mechanism is substantiated by variousobservations. When a polyamide is heated for some time in anoxygen-containing atmosphere it shows an increasing oxygen absorption, afairly constant peroxide concentration, a decrease of the number ofamine end groups and a corresponding increase of the pyrroleconcentration, as can be seen from the following table:

HEATING OF POLYHEXAMETHYLENE ADIPAMIDE 150 C. IN AIR Oxygent PeroxideOoncentra- Pyrrole eon- Time (Hours) absorption concentration of aminetents Specific (g./kg.) tion end groups absorption (mg/kg.) (mMol/kg.)at 530 my 1 1 Determined in a 0.4%

polyamide solution in 90% formic acid dyed with 1%dimethyl-amino-benzaldehyde.

ployed as a component of the stabilizer, is added as chain terminator.

The polyhexamethylene adipamide compositions are prepared as follows: A50% aqueous solution of hexamethylene diamine adipate is evaporateduntil a concentration of 75 to is achieved and is then heated instabilizers, of any optical brightening agents can take place at variousstages during manufacture. In Examples I to III the phenolic compound,the phosphorus compound, and the manganese salt are mixed with the 50%solution of hexamethylene diamine adipate. The titanium dioxide, in theform of a 20% aqueous dispersion, and, if desired,

In Examples V and the 50% hexamet after the Water has been evaporated.

The polycaprolactam composition is made by warming caprolactam to C.,mixing it with 1% of water and heating it in an autoclave for 2 hours at250 C. Then dioxide or optical brightening agents can take place at InExample IV the manganese salt are added to the caprolactam together withthe 1% of water, and the carboxylic acid anhydride,

dissolved in a little ethanol, is added when the pressure has beenreleased.

From the polyamide compositions obtained, fibres are melt-spun in theusual manner, and compared with containing no stabilizer ferentcombinations of only three of the four stabilizers used in the presentinvention. The relative viscosity is determined at 25 C. on an 11%solution of the polyamide composition in 90% formic acid. The heatingtest is carried out with a Thermotest Rhodiaceta developed by RhodiacetaS.A., Paris, and made by Societe pour la Difiusion dAppareils de Mesureet de Controle, S.A., Tassin-la-Demi-Lune, Rhone, France. In this testsmall hanks of yarn are brought into contact during 60 seconds withheated metal plates having a temperature between 210 and 240 C., afterwhich the colour of the yarn is judged visually.

When carrying out the irradiation test, fibres not containing an opticalbrightening agent are used, because these agents are decomposed by lightand may become yellow themselves. The fibres are exposed to sunlight ofan intensity equal to rating 7 of the blue standard, according to test95810 of the Swiss Standards Institution (SNV), and subsequently kept inthe dark for three months, after which the colours of the light-exposedand the unexposed fibres are compared.

All percentages of quantities of materials mentioned in the followingexamples are by weight of the total weight of the polyamide composition.

Example I A polyamide composition is made from kg. of hexamethylenediamine adipate containing 47.3 g. (=l.l%) of titanium dioxide and, asstabilizers, 2.15 g. 0.05%) of 2,5-di-tert-butyl-hydroquinone, 4.3 g.0.1%) of sodium hypophosphite, 0.645 g. (=0.015%) of manganous lactate,equal to 30 parts of manganese per million parts of polyamide, and 23.65g. (=0.55%) of benzoic acid anhydride. The polyamide chips obtained arepure white.

Polyamide chips made for comparison in the same manner containing 1.1%of titanium dioxide and 0.17% of acetic acid as chain terminator, but nostabilizing agents, have a distinct ivory colour.

Example II Fibres are melt-spun from a polyamide composition made from 5kg. of hexamethylene diamine adipate containing 47.3' g. (=1.1%) oftitanium dioxide, 4.3 g. (=0.1%) of an optical brightening agent UvitexMP made by Ciba A.G., Basel, Switzerland, a stilbene derivative, and, asstabilizers, 2.15 g. 0.05%) of 2,5-di-tertbutyl-hydroquinone, 4.3 g.(=0.1%) of sodium hypophosphite, 0.645 g. (=0.015%) of manganouslactate, equal to 30 parts of manganese per million parts of polyamide,and 23.65 g. (=0.55%) of benzoic acid anhydride. The relative viscosityof the fibres is 31.5, their tensile strength 5.9 g./denier, and theirelongation at break 27.6%. No difference could be detected in the colourof the fibres before and after heating to 225 C.; in both cases thefibres are pure White.

Fibres made in the same manner, but without the addition of an opticalbrightening agent, are subjected to the irradiation test. Bothv thelight-exposed and the unexposed fibres show the same whiteness.

Fibres made for comparison in the same manner containing titaniumdioxide and 0.17 of acetic acid as chain terminator, but no stabilizingagents, have a relative viscosity of 32.2, a tensile strength of 5g./denier, and an elongation at break of 27.1%. While the colour of thefibres is originally ivory-white, it becomes strongly yellow when thefibres are heated to 225 C. or when they are subjected to theirradiation test.

Fibres are made for comparison in the same manner containing 1.1% oftitanium dioxide and only three stabilizers, i.e.:

(a) 0.1% of sodium hypophosphite, 0.015% of manganous lactate, equal to30 parts of manganese per million parts of polyamide, and 0.55% ofbenzoic acid anhydride, or

(b) 0.05% of 2,5-di-tert-butyl-hydroquinone, 0.015% of manganouslactate, equal to 30 parts of manganese per million parts of polyamide,and 0.55 of benzoic acid anhydride, or

(c) 0.05% of 2,5-di-tert-butyl-hydroquinone, 0.1% of sodiumhypophosphite, and 0.55 of benzoic acid anhydride, or

(d) 0.05% of 2,5-di-tert=butyl-hydroquinone, 0.1% of sodiumhypophosphite, and 0.015% of manganous lactate, equal to 30 parts ofmanganese per million parts of polyamide (adding 0.17% of acetic acid aschain terminator) While the colour of all four kinds of fibres isoriginally ivory white, it becomes more or less distinctly yellow whenthe fibres are heated to 220 C. or when they are subjected to theirradiation test.

Example Ill Fibres are melt-spun from a polyamide composition made from5 kg. of hexamethylene diamine adipate containing 1.1% of titaniumdioxide, 0.1% of Uvitex MP, and, as stabilizers, 0.05% of2,5-di-tert-butyl-hydroquinone, 0.25% of triphenyl phosphate, 0.01% ofmanganous oxalate, equal to 38 parts of manganese per million parts ofpolyamide, and 0.55 of hexahydrophthalic acid anhydride. The relativeviscosity of the fibres is 34.5, their tensile strength 6.2 g./denier,and their elongation at break 24.1%. The colour of the fibres bothbefore and after heating to 225 C. is a pure white.

Example 1V Fibres are melt-spun from a polyamide composition made from 5kg. of cap -rolactam containing as stabilizers 0.05% of2,5-di-tert-butyl-hydroquinone, 0.1% of sodium hypophosphite, 0.01% ofmanganous oxalate, equal to 38 parts of manganese per million parts ofpolyamide, and 0.225% of benzoic acid anhydride. The relative. viscosityof the fibres is 28.5, their tensile strength 5.0 g./ denier, 'and theirelongation at break 15.3%. The colour of the fibres both before andafter heating to 210 C. or when subjected to the irradiation test is apure white.

Fibres made for comparison in the same manner containing 0.17 of aceticacid as chain terminator and no stabilizing agents are originally white,but become strongly yellow when heated to 210 C.

Example V Fibres are melt-spun from a polyamide composition made from1000 kg. of hexamethylene diamine adipate containing 1.9% of titaniumdioxide and, as stabilizers, 0.05% of 2,2-methylenebis-(4-methyl-6-tert-butyl-phenol), 0.3% of triphenyl phosphate, 0.01%of manganous oxalate, equal to 38 parts of manganese per million pantsof polyamide, and 0.4% of benzoic acid anhydride. The relative viscosityof the fibres is 36.6, their tensile strength 5.8 g./denier, and theirelongation at break 31.1%. The colour of the fibres both before andafter heating to 225 C. is a pure white. When the fibres are subjectedto the irradiation test, both the light-exposed and the unexposed fibresshow .the same whiteness.

Example VI Fibres are melt-spun from a polyamide composition made from1000 kg. of hexamethylene diamine adipate containing 1.9% of titaniumdioxide and, as stabilizers, 0.05% of 4,4 bu tylidenebis-(6-tert-butyl-m-cresol), 0.3% of triphenyl phosphate, 0.01% ofmanganous oxalate, equal to 38 pants of manganese per million pants ofpolyamide, and 0.4% of benzoic acid anhydride. The relative viscosity ofthe fibres is 34.5, their tensile strength 7.2 g./denier, and theirelongation at break 16.6%. The colour of the fibres both before andafter heating to 225 C. or when subjected to the irradiation test is apure white.

I claim:

1. Synthetic polyamide compositions which are substantially free fromcolour and of good stability against discoloration by heart and light,in which have been inpolycontden's-ation (1) between 0.02 and 0.2% of athermally stable phenol containing at least one tertiary-butyl groupselected from the class consisting of 2,S-di-tert-butyl-hydroquinone,2,2-methylene-bis-(4-methyl-6-tert-butyl-phenol), 2,2methylenebis-(4-ethyl-6- tert-butyl-phenol), and 4,4'-butylidene bis-(6-tert-butyl-m-cresol), (2) between 0.05 and 0.5% of a compoundselected from the class which consists of salts and esters of inorganicphosphorus oxy-acids, (3) between 20 and 80 parts of manganese permillion parts of said polyamide composition in the form of a compoundselected from the class consisting of manganous lactate, manganousoxalate and manganous hypophosphite, and 1% of a mononuclear cyclicorganic acid anhydride selected from the group which consists of theanhydrides of benzoic acid and hexahydrophthalic acid, the proportionsbeing based on the total weight of the composition.

2. Synthetic polyamide textile fibres which are substantially firee fromcolour and of good stability against discoloration by heat and light, inwhich have been incorporated during polycondensation 1) between 0.02 and0.2% of a thermally stable phenol containing at lea-st onetentiary-bu'tyl group selected from the class consisting of2,S-di-tert-butyl-hydroquinone,2,2-methylene-bis-(4-methyl-6-tert-bu.tyl-phenol), 2,2methylenebis-(4ethyl-6- tert-butyl-phenol), and 4,4-butylidene bis-(6-tert-butyl-m-cresol), (2) between 0.05 and 0.5% of a compoundselected from the class which consists of salts and estens of inorganicphosphorus oxy-acids, 3) between 20 and pants of manganese per millionparts of consists and hexahydrophthalic on the total weight ofReferences Cited by the Examiner UNITED STATES PATENTS 2,510,777 6/1950Gray 260*78 2,705,227 3/1955 Stamatofi 260-4575 2,849,446 8/1956Sullivan 45.95 2,966,476 12/1960 Kralove et al. 26045.95 3,117,9481/1964 Notarbatolo et al. 260-45.75

FOREIGN PATENTS 495,790 11/1938 Great Britain. 955,259 6/ 1949' France.1,052,679 3/1959 Germany. 1,220,968 11/1960 France.

OTHER REFERENCES Perry, N. L., Stabilizers, 1963 Modern PlasticsEncyclopedia, Vol. 40, No. 1A, September 1962, pp. 502 505, p. 502relied upon.

LEON J. BERCOVITZ, Primary Examiner. G. W. RAUCHF USS, AssistantExaminer.

1. SYNTHETIC POLYAMIDE COMPOSITIONS WHICH ARE SUBSTANTIALLY FREE FROMCOLOUR AND OF GOOD STABILITY AGAINST DISCOLORATION BY HEAT AND LIGHT, INWHICH HAVE BEEN INCORPORATED DURING POLYCONDENSATION (1) BETWEEN 0.02AND 0.2% OF A THERMALLY STABLE PHENOL CONTAINING AT LEAST ONETERTIARY-BUTYL GROUP SELECTED FROM THE CLASS CONSISTING OF2,5-DI-TERT-BUTYL-HYDROQUINONE,2,2''-METHYLENE-BIS-(4-METHYL-6-TERT-BUTYL-PHENOL),2,2''-METHYLENEBIS-(4-ETHYL-6-TERT-BUTYL-PHENOL), AND 4,4''-BUTYLIDENEBIS(6-TERT-BUTYL-M-CRESOL), (2) BETWEEN 0.05 AND 0.5% OF A COMPOUNDSELECTED FROM THE CLASS WHICH CONSISTS OF SALTS AND ESTERS OF INORGANICPHOSPHORUS OXY-ACIDS, (3) BETWEEN 20 AND 80 PARTS OF MANGANESE PERMILLION PARTS OF SAID POLYAMIDE COMPOSITION IN THE FORM OF A COMPOUNDSELECTED FROM THE CLASS CONSISTING OF MANGANOUS LACTATE, MANGANOUSOXALATE AND MANGANOUS HYPOPHOSPHITE, AND (4) BETWEEN 0.2 AND 1% OF AMONONUCLEAR CYCLIC ORGANIC ACID ANHYDRIDE SELECTED FROM THE GROUP WHICHCONSISTS OF THE ANHYDRIDES OF BENZOIC ACID AND HEXAHYDROPHTHALIC ACID,THE PROPORTIONS BEING BASED ON THE TOTAL WEIGHT OF THE COMPOSITION.